[Ap Chem]Significant figures

Test Preparation AP Test Preparation
1

<p>It says in my TPR prep book:</p>

<p>"When multiplying and dividing, the result should have the same number of significant figures as the number in the calculation with the smalelst number of significant figures."</p>

<p>But what about 31 X 0.7=????</p>

<p>isn't the answer 21, rather than 21.7???</p>

<p>i thought the result was supposed to match with the LEAST accurate figure.</p>

<p>help me out here.</p>

<p>Oh, and about the calculator... does the calculator have to be a graphing one??? or is it enough to be just a scientific one? or can it just be one of those really basic ones, that can only calculate sin, tan, cos, square roots, etc....</p>

2

<p>1.) i'm 95% sure it's basic calculators only
2.) 0.7 is 1 sig fig, so shouldn't the answer be 20? or was it 21? bleh i'm not good at sig figs and nomenclature :&lt;/p>

<p>either way, the answer can't be 21.7</p>

3

<p>31 x 0.7 should be 20 (Note: not 20.)</p>

<p>31 + 0.7 should be 32</p>

4

<p>yea slorg that's what i thought, it should be 20, not 21</p>

5

<p>oops, i rounded up:p</p>

6

<p>Yea guys I was doing one of the free response and i took the -log(ans) and got 4.13 for a ph (it was 4.1266 and there were 3 sig figs.) The problem is on collegeboard it said the answer was 4.12. what the heck..</p>

7

<p>WAIT~!!! isn't my calculation right?? aren't you supposed to actually multiply the figures and then round the part that isn't significant??</p>

<p>i.e.</p>

<p>31 X 0.7 = 21.7
since the most inaccurate figure is 31(to the unit digit)
you round 0.7 and get 22 </p>

<p>i think i learned it this way...correct me if i'm wrong</p>

8

<p>I caught some errors on the answers for the FRQs using sigfigs also. I emailed the guys at collegeboard last year and they said they aren't too strict on sig figs, as long as you get them within +-1 of the correct amount. (If the answer should have 4 sig figs, and you put an answer with 3, 4, or even 5 sig figs this is still okay)</p>

9

<p>22 is two sig figs jac.</p>

<p>.7 is one sig fig</p>

<p>20 (w/out a decimal) is one sig fig.</p>

<p>gyros - you may have slightly rounded, or the book may have slightly rounded somewhere or the other...... don't worry about it - all answers can be off by +- 1 decimal point.</p>

<p>phoenix - that may be right, but are you sure it isn't talking about the answer it self?</p>

<p>like if the answer is 4.12, but you have 4.11 or 4.13, you still get full credit? I think that's how it is, may also be like your example w/ the sig figs.</p>

10

<p>don't worry about sig figs..they will be the least of your worries :)</p>

11

<p>My chem teacher said that they aren't counting off for sig figs anymore?? don't know whether this is true or not.</p>

12

<p>I think they take away a point once you are off by one sigfig.</p>

13

<p>college board gives you room for a + or - 1 sig fig error</p>